The first 440 bytes contains the bootstrap code area, which takes care of starting up the operating system present on the active partition. Then, it is the disk signature, a 4-byte number that is randomly generated when the MBR is first created. It is an identifier which applies to the whole hard drive (not a single partition). After that, there are a couple of bytes set to null, and next, the partition table.

The partition table is made up of four entries of 16 bytes each which define the position and size of the sectors (LBA or Logical Block Addressing). In order to work around the problem of having just four partitions, these primary partitions can contain an arbitrary number of logical partitions. This schema can lead to problems, because some operating systems can only boot from primary partitions.

On the other hand, how do I work out the figure of 2.2 TB as top size for a partition? In conjunction with the universal sector size of 512 bytes and the 32-bit LBA pointers used by MBR partitions, you have ( 2^32 ) - 1 sectors * 512 bytes per sector.

(Also say that the MBR ends with the sequence of two bytes 0x55AA).

On account of the current size of hard drives and RAID technologies, the problem is really serious and will become more severe over time. In order to overcome it, the GUID partition table (GPT) is the natural successor to the MBR partition table.

GPT, supported on Linux since the 2.6.25 kernel version, uses 128-byte LBA modern tables, so therefore it is possible to have hard drives up to 8 ZB addressable for a disk with a 512-byte sector size. In addition, GPT can manage up to 128 partitions, so there is no need for extended or logical partitions. If you are interested, you can read up more about this topic on the Internet, since the aim of this article is to put forward how to manage this technology on Linux (also mention that for my tests, I used an Ubuntu Server 12.04 distribution).

First of all, point out that fdisk does not work with this partitioning scheme, but the good news is that can be got over with other Linux tools, such as parted. Keeping on with the tests, I have added a second hard drive to my system.

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About the author...

Javier Andrés Alonso has got a Master's Degree in Telecommunication Engineering and a Bachelor's Degree in Telecommunication Technical Engineering (specialising in Telematics), from the Polytechnic School of the University of Alcalá de Henares.